This invention relates to automatic transmissions for vehicles and, more particularly, to transmissions providing drive to both the front and rear wheels of the vehicle.
All-wheel drives and four-wheel drives are commonly used in many passenger vehicles today. These vehicles generally include sport utility vehicles; however, some passenger type vehicles are also equipped with all-wheel drive powertrains. In the all-wheel drive powertrain, the engine and transmission are generally forward on a vehicle, and a transfer case or drop box is attached to the rear of the transmission and receives input drive from the conventional output shaft of the transmission. The transfer case generally includes a chain or gear drive from one axis to another axis to permit the front-wheel drive or a gear arrangement between the transmission output shaft which is the input to the transfer case and the second axis which contains the front-wheel drive power shaft.
The transfer case, as previously mentioned, is secured to the rear of the transmission and therefore extends the longitudinal length of the powertrain, such that additional space under the vehicle is required to accommodate the engine, transmission, and transfer case. This generally means the tunnel hump is extended rearwardly in the vehicle between the driver and passenger seats. The powertrain may also require additional space to accommodate the positioning of the power shaft driving the front wheels. This space may also intrude into the passenger compartment, thereby reducing the amount of room or the volume within the passenger compartment.
It is an object of this invention to provide an improved powertrain for an all-wheel drive vehicle.
In one aspect of the present invention, the transmission includes an input shaft extending longitudinally of the transmission housing and a grounding shaft circumjacent the input shaft also extending longitudinally within the transmission case.
In another aspect of the present invention, a plurality of torque transmitting mechanisms, both rotary and stationary, are disposed rearwardly of the torque converter and forwardly of the output shaft.
In yet another aspect of the present invention, the stationary torque transmitting mechanisms are selectively connectable with the grounding shaft of the transmission.
In still another aspect of the present invention, the transmission includes a ratio gear set disposed rearwardly of the torque transmitting mechanisms and incorporating a differential gear set at the output end of the transmission.
In a further aspect of the present invention, the differential gear set incorporates both an output drive to the rear wheels and an output drive to the front wheels.
In a yet further aspect of the present invention, the output drive to the front wheels is comprised of a rotatable housing, which extends forwardly outboard of and surrounding the planetary gear set and the torque transmitting mechanism.
In a still further aspect of the present invention, the rotatable housing is drivingly connected with a transfer mechanism, which is disposed between the torque converter and the torque transmitting mechanisms of the transmission.
A powertrain, incorporating the present invention, includes an engine, a torque converter drivingly connected with the engine, a planetary gear arrangement including a plurality of planetary gear sets and torque transmitting mechanisms, an output differential mechanism drivingly connected with the planetary gear sets, and providing both front and rear wheel output drive mechanisms.
The output drive mechanism of the differential gear set, which is directed to the front wheels, includes a rotatable housing, which encloses or is disposed circumferentially of the torque transmitting mechanisms in the planetary gear set. This front wheel drive structure includes a transfer mechanism which transfers the drive from the axis of the transmission to an axis for the front-wheel drive power shaft.
The torque transmitting mechanisms, which are disposed interiorly of the rotatable housing, include a plurality of rotating torque transmitting mechanisms or clutches, and a plurality of stationary torque transmitting mechanisms or brakes. The brake mechanisms are disposed forwardly with relation to the powertrain of the rotary torque transmitting mechanisms.
A grounding shaft to which the brakes are operatively connectable is disposed circumjacent and coaxial with an input shaft. The input shaft transfers power from the torque converter to the rotating torque transmitting mechanisms and one member of the planetary gear set. The grounding shaft is connectable between the brakes and housings which are surrounding the torque transmitting mechanisms and connectable with various members of the planetary gear set. A portion or some of the rotary torque transmitting mechanisms are connectable with at least one of these housings.
The transfer mechanism is comprised of a pair of sprockets, one of which is rotatably mounted on the grounding shaft and the other is rotatably mounted in a housing outboard of the transmission. A chain drive is connected between the sprockets. The outboard sprocket member is drivingly connected with a shaft which transfers power forwardly to the front wheels of the vehicle. Alternatively, a gear drive mechanism may be utilized in place of the chain and sprocket mechanism.